getSQLStates

Adds extra SQLState code that Derby JDBC Driver uses. In JDBC 4.0,
SQLState will follow either XOPEN or SQL 2003 convention. A compliant
driver can be queries via DatabaseMetaData.getSQLStateType() to detect
the convention type.
This method is overwritten to highlight that a) the SQL State is ideally
uniform across JDBC Drivers but not practically and b) the overwritten
method must crate a new list to return as the super classes list is
unmodifable.